The present invention relates generally to systems for controlling fluid flow. More particularly, the present invention relates to systems for infusing fluids in and withdrawing fluids from patients undergoing medical care.
Several treatments for disease require the removal of blood from a patient, processing the one or more components of the blood and return of the processed components for a therapeutic effect. Those extracorporeal treatments require systems for safely removing blood from the patient, separating it into components, where necessary, and returning the blood to the patient.
Photopheresis is one treatment involving the separation of white cells from the blood, addition of a photoactivatable drug, and U.V. irradiation of the white cells before re-infusion to the patient. In known photopheresis systems, such as system 100 shown in FIG. 1, blood fluids are pumped by peristaltic roller pumps 110. In system 100, a complex tubing set is used to couple a patient 120 to an extracorporeal blood treatment system which includes a cell separator 130, a white blood cell photoactivation chamber 140, a saline bag 150a, an anti-coagulant bag 150b and a waste bag 150c. Valves 160, bubble chambers 170, air detectors 180, and pressure sensors 190 are interconnected to the tubing set for monitoring and controlling fluid flow within the system. Complex tubing sets, such as that shown in FIG. 1, have the potential to cause cell damage under high outlet pressure conditions. Blood has also been pumped with discrete pump chambers and valves which also require complex tubing sets. Such discrete pump chambers and valves are considered to be less damaging to cells under high outlet pressures.
A very real advancement in photopheresis systems would result if the size and complexity of the tubing in systems such as that shown in FIG. 1 could be reduced, even at the cost of a more complex blood driving system, since the blood driving system represents permanent reusable equipment, whereas the tubing set must be replaced or disposed of after each treatment session. A similar result has been accomplished with peritoneal dialysis systems, where the flow of dialysate is controlled entirely with diaphragm pumps and valves driven by air pulses delivered to a molded cassette through a plastic membrane. See for instance several patents by Dean Kamen, including U.S. Pat. No. 5,178,182, issued Jan. 12, 1993 and U.S. Pat. No. 5,634,896 issued Jun. 3, 1997, which are incorporated herein by reference.
The cassette contains all components of a previously complex tubing set, except for the lines to the patient and short delivery lines from the dialysate containers. The air pulses delivered to the cassette are controlled by continually analyzing the pressure changes in the air delivered to the diaphragm pumps, processing the pressure changes through a computer, and making continual corrections as a result. The resulting peritoneal dialysis system is able to accurately measure the fluid delivered, but is unable to provide a fixed steadiness of flow rate. In contrast to peritoneal dialysis systems, systems such as photopheresis systems, which involve continuous blood cell separation, require both a very steady flow rate, as well as the ability to control the fluid flow rate. Furthermore, such a system may tend to promote clotting, hemolysis and cell lysis when pumping blood, as opposed to its intended fluid, dialysate which contains no cellular components.
An apparatus according to the present invention controls movement of fluids during an extracorporeal blood treatment session. It comprises a hollow enclosure having a plurality of fluid input ports for receiving the fluids into the enclosure and a plurality of fluid output ports for expelling fluids from the enclosure. Internal fluid passageways within the hollow enclosure couple together the fluid input ports, and the fluid output ports. At least one internal valve is disposed within the hollow enclosure and connected to at least one of the internal fluid passageways for controlling movement of the fluid within the hollow enclosure during the extracorporeal blood treatment session. A filter in the hollow enclosure filters the fluids.
Preferably, the filter comprises a first chamber and a second chamber within the enclosure which are separated from each other by a filter media, having a pore size of 200 to 400 microns, and most preferably about 200 microns. A filter media of woven mesh, such as a woven polyester such as DACRON brand is preferred. One or both of the filter chambers can be partially formed by an elastomeric membrane material outer surfaces of the hollow enclosure. Preferably, some means is provided to evacuate air from the filter chambers.
A method according to the present invention for controlling movement of fluids during an extracorporeal blood treatment comprises the steps of: extracting blood from a patient and admitting the blood into a hollow enclosure having a plurality of fluid input ports for receiving the blood into the enclosure, a plurality of fluid output ports for expelling the blood from the enclosure and a plurality of internal fluid passageways disposed within the hollow enclosure for coupling together the fluid input ports, the fluid output ports; directing flow of the blood through selected ones of the fluid passageways with at least one internal valve disposed within the hollow enclosure; and filtering the blood through a filter in the hollow enclosure.
Preferably, the first chamber is at least partially formed of a first layer of flexible membrane material disposed on a first outer surfaces of the hollow enclosure and the method further comprises the step of measuring the pressure in the first chamber by measuring the pressure against the flexible membrane. The blood is preferably returned to the patient from the hollow enclosure, and the filtering step preferably closely precedes the step of returning the blood to the patient so as to reduce the possibility of a clot forming in the enclosure and returning to the patient.